Shale formations are known for their chemical interactions with water based muds which may result in swelling, bit balling or even closure of the wellbore. As a result, eco-friendly water based fluids with inhibitive characteristics are required for drilling through shale formations. The aim of this study is to provide a deeper insight into drilling through shale formations by providing few approaches for different circumstances. Many inhibitors developed so far are introduced with their mechanism of shale inhibition presented. It appears that silicate based muds and thermally activated mud emulsion (TAME) are the best option to mitigate shale related issues, but more studies are required to provide a permanent solution for this very complicated issue, especially under HPHT conditions.
Rheological and filtration properties of water based muds play vital roles in having a good drilling efficiency through hostile and harsh environments. However, there are many occasions in which controlling the variation of mud properties due to disintegration of additives is barely possible resulting in stuck pipe, kick incident or even loss of wells. The aim of this study is to propose an approach to enhance filtration characteristics of water based muds using nanoparticle additives. The results obtained from zeta potential measurements indicated that bentonite and nanosilica particles are both negatively charged with the values of-28 mV and-27 mV at the pH of 8 respectively. Evaluating rheological parameters of different mud samples revealed that the unmodified nanosilica causes reduction in the yield point of the samples rising concerns in the cuttings carrying capacity of drilling fluids. This issue was resolved by modifying the surface charge of nanosilica using a cationic surfactant. Filtration tests conducted under LPLT and HPHT conditions indicated that adding modified nanosilica into the mud samples results in formation of a thin and low permeability filter cake which can be a great asset in drilling through high permeable and small pore throat formations.
A systematic and careful analysis of changes in the magnitude of geomechanical parameters is essential to mitigate the risk of leakage from CO2 storage sites. However, depending on rocks and storage sites, these changes might be different due to chemical reactions taking place, especially when it comes to saline aquifers. There have only been few studies carried out in the past to evaluate the maximum sustained pressure of rocks being exposed to these chemical interactions. However, more studies are still required to evaluate the strength of the storage medium or seals when different kinds of rocks and fluids (fresh water or brine) are included in the hostile environment of a storage site. In this paper, attempts were made to evaluate changes in the variation of geomechanical parameters of the Berea sandstone during and after the injection of supercritical CO2 in a short period of time. The results obtained indicated that the presence of brine in the pore space during injection enhances the severity of geochemical reactions, causing reductions in the magnitudes of elastic parameters including shear modulus. Having a good look into the SEM images of the sample before and after exposure to scCO2 indicated that these changes can be attributed to the dissolution/fracturing of calcite and clays in the matrix of the sample. Although findings were provided based on the pulse measurements tests, more studies are required to have a deeper understanding as to how geochemical reactions may cause difficulties during and after injection into a storage site.
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